Meteorology 3000- Mountain Weather and Climate

Assignment 5. Due September 21. 20 points

The goal of this assignment is to compute components of the surface energy balance for one location that is exposed to direct sunlight and relatively flat. You will work in teams of 4-5 people to collect observations using several different sensors. Tables and text must be emailed or typed and turned in to me by the beginning of class next Wednesday.

Stefan-Boltzmann Law: IR = emissivity x constant x TxTxTxT. The constant is 5.67x10(-8) W/(m2 K4).

Data Collection

2. Because of the slow time response of the dial thermometers, immediately decide upon an unique location in the vicinity of the INSCC building for your group. Insert one dial thermometer into the soil so that the dial is about an inch above the ground. Cover the thermometer with a styrofoam cup or piece of cardboard so that it is not exposed to direct solar radiation.

2. Each person has a Kestrel hand held instrument to measure temperature, wind speed and dewpoint. Record measurements of these quantities from at least two sensors at regular intervals (every couple of minutes for 10 minutes) at your location at roughly 1.5 m above ground level. Record measurements of soil temperature at the same time.

3. Using the hand held IR gun, record the temperature of the surface at the same time that you are taking other measurements. Since you have to share the IR sensor, you will not have as many simultaneous observations of IR temperature.

Analysis

5. Summarize the characteristics of your site: soil type, solar zenith angle, aspect, slope, etc.

6. It is very important to organize the data collected in a coherent table using metric units (all temperature observations should be first in C then in K in a separate column, wind in m/s). Average all the observations collected during your 10 minute observing period; discard extreme outliers.

Each of the following should be displayed in separate columns.

7. Using the Internet, text or other resources, estimate the incoming solar radiation (w/m2) at the top of the atmosphere at noon for the latitude of Salt Lake City. We are close to the autumnal equinox at this time of year.

8. Estimate from the figure in the text the albedo of your surface (take the midpoint value for the relevant soil type). Estimate the absorbed solar radiation (w/m2) based on the albedo and results from 7.

9. Depending on the sky conditions, we will estimate the temperature of the atmosphere radiating to the earth's surface. Once that temperature is estimated, use the sounding for the Salt Lake City Airport from Wyoming to estimate the pressure level and height from which the atmosphere is emitting radiation back to the surface. Using the Stefan Boltzmann Law and assuming the atmosphere is a blackbody (emissivity equal to 1), how much energy is being received at the earth's surface from the atmosphere (w/m2)?

10. Estimate the emissivity of the surface from the figure in the text (take the midpoint value for the relevant soil type). Estimate the infrared radiation (w/m2) emitted upwards from the surface from your measurements of the surface temperature obtained from the IR gun.

11. Estimate the net radiation (w/m2) of the surface (absorbed solar #8 + atmosphere IR #9 - surface IR #10). Is the surface gaining or losing energy at this time? What effects are we ignoring here? Hint: look around your site.

12. Estimate the sensible heat flux using the following "bulk" formula: H (w/m2) = 1.73 x wind speed (m/s) x (surface temperature from IR gun minus air temperature) (C). Is the surface losing to or gaining energy from the atmosphere?

13. Estimate the latent heat flux using the following "bulk" formula: L (w/m2) = 3.61 x wind speed (m/s) x (surface vapor pressure minus air vapor pressure) (mb). Use the table of vapor pressure as a function of dew point to determine the air vapor pressure. Is dew observed at the surface? If not, assume that the surface vapor pressure is a few mb higher than the air vapor pressure. Is the surface losing to or gaining energy from the atmosphere by evaporation/condensation?

14. Compute the residual heat storage (w/m2) into the soil by summing the net radiation, sensible heat flux, and latent heat flux (#11 - #12 - #13). Would you expect the soil beneath the surface to be warming or cooling at this time?

15. Compute the difference, surface temperature (from dial thermometer) minus soil temperature from IR gun (C/K). Is energy being stored in the soil or is heat being conducted from the soil to the surface? How do your results in #14 and #15 compare? Are they consistent?

Summary

16. To what extent do your results agree with the summary figures in the text on the surface energy balance? How would you explain any differences?

17. How would your results be different if the data were collected at night?